ADDED: context-based command for inserting new clauses or terms

ADDED: context-based command for inserting new clauses or terms

* sweeprolog.el (sweeprolog--forward-hole, sweeprolog--backward-hole):
new functions.
(sweeprolog-forward-hole): new command.
(sweeprolog-end-of-predicate-definition,sweeprolog-insert-clause,
sweeprolog-maybe-insert-next-clause,
sweeprolog-maybe-define-predicate): new functions.
(sweeprolog-insert-term-functions): new hook.
(sweeprolog-insert-term-dwim): new command.
(sweeprolog-mode-map): bind new commands.
* sweeprolog-tests.el (dwim-define-predicate): new test case.
* README.org (Context-Based Term Insertion): new section.